1. Field of the Invention
The invention concerns an improved drum pulley of the general type described in U.S. Pat. No. 2,973,654, in which hub parts are connected by means of tapered clamping assemblies to a drum shaft.
2. The Prior Art
A drum pulley arrangement is known from U.S. Pat. No. 2,973,654, in which a drum pulley is secured to a shaft by means of flanged hubs, the flange of each hub attached to a part of the pulley and the hub parts surrounding the shaft. The external circumference of the hub part is conical, with the heavier wall thickness of the cone being located on the side of the flange. A tapered ring is applied to the external circumference of the hub part and may be tightened against the flange by means of threaded bolts, while resting with its inner circumference on the outer circumference of the hub part. The tightening of the threaded bolts radially compresses the hub part and thus, clamps it fixedly on the shaft.
Drum pulleys of this type are used in considerable sizes. For example, drum pulleys with diameters up to 1,500 mm, lengths to 3 m and shaft diameters to 500 mm are employed in the long conveyors used in lignite coal surface mining. Drives of up to 1000 kW are transmitted by these shafts. Because the shafts of drum pulleys of this size are supported on bearings outside the drum and under certain circumstances must additionally provide space outside the bearings for coupling gears or other means of coupling to the drive, very long and heavy structural parts are involved. The fabrication of such parts entails considerable expense.
Another problem consisted heretofore of the fact that is was necessary to design the shaft with a greater thickness than required by the bending moment acting upon it. Because the drum pulley itself absorbs part of the bending stress generated by the tension of the conveyor belt, the shaft inside the drum pulley is not required to withstand the entire bending moment. The radial forces transmitted by the hubs are introduced immediately next to the outer bearings so that the principal bending stress is applied between the hubs and the bearings. Large shaft diameters are therefore required in this location only. Another reason for the excessive dimensioning of the shaft practiced heretofore is to be found in the self-aligning roller bearings conventionally used to support the shaft. Since the load bearing capacity increases with rising diameters, larger bearings were frequently employed to increase this capacity and the diameter of the shaft adapted to the bearings, while the shaft diameter could have been thinner from the standpoint of the bending moment. Milling to reduce the diameter of the portion of the shaft located inside the drum would merely add to the expense.